1. Field of the Invention
This invention relates to an alloy suitable for use in exhaust valves of various internal-combustion engines.
2. Related Art Statement
In order to attain high power of the engines, there is recently a tendency that the number of valves are set into three per one cylinder in the conventional SOHC (single overhead cam shaft type) engines or four per one cyclinder in DOHC (double overhead cam shaft type) engines instead of SOHC engines. With such a tendency, the reduction in a diameter of an engine valve is rapidly promoted in order to satisfy the requirement on high revolution and high power of the engines. On the other hand, high manganese austenite steel of SUH 36 (Fe-8.5Mn-21Cr-4Ni-0.5C-0.4N) has hitherto been used as a material of an exhaust valve in gasoline engines, diesel engines or the like.
However, it is demanded to adopt materials for exhaust valves having a high temeprature strength higher than that of SUH 36 in accordance with the tendency of a valve diameter reduction as mentioned above.
As the high strength material for exhaust valves, there have hitherto been known nickel-based heat resistant alloys of NCF 751 (Ni-15.5Cr-1Nb-2.3Ti-1.2Al-7Fe) and NCF 80A (Ni-19.5Cr-2.5Ti-1.4Al). They are used as a material requiring no stellite surfacing, but are inexpressible to sufficiently satisfy the high temperature strength required by the above diameter reduction.